It is not easy to sample electrical activity in very tightly defined areas of animal tissue, and it is not easy to stimulate very tightly defined areas of animal tissue. When further constraints are imposed, such as the desire to minimize trauma to the tissue in insertion of leads for such sampling and stimulation, and the need to be able to insert a lead only once and yet to preserve great flexibility in later use of the lead, the task that was not easy becomes even more difficult.
A prior-art type of stimulation and sensing is shown in FIGS. 1A and 1B. FIG. 1A shows a prior-art pacer lead configuration using a single conductor in a lead 13. The “can” 12 contains drive or sensing electronics that are external to electrode locations 14. The can 12 and lead 13 (with its electrode locations 14) is implanted within tissue 17 of an animal, below surface 11 such as a dermal surface.
An impedance model for the tissues 17 assumes localized impedances 18 physically nearby to the electrode areas 14, and more generalized impedance 19, together defining a return path to the can 12.
FIG. 1B shows a prior-art pacer lead configuration using two conductors 15, 16 in a lead 13. Electrodes at the electrode areas 14 may be selectively communicatively coupled with conductors 15, 16. Drive voltages from the can 12 pass through the conductors 15, 16 to particular electrodes in area 14. The drive voltage will stimulate a region 20 of the tissue 17.
The selective coupling of electrodes to lead conductors may be achieved for example by means of circuitry and techniques set forth in a multiplex system (e.g., as described in United States Patent publication no. US 20040254483 entitled “Methods and systems for measuring cardiac parameters”; US patent publication number US 20040220637 entitled “Method and apparatus for enhancing cardiac pacing”; US patent publication number US 20040215049 entitled “Method and system for remote hemodynamic monitoring”; US patent publication number US 20040193021 entitled “Method and system for monitoring and treating hemodynamic parameters; and provisional application No. 61/121,128 filed Dec. 9, 2008), which disclosures are hereby incorporated herein by reference for all purposes.
It will be appreciated that the same physical structures of these two figures may likewise be employed to permit sensing of electrical activity in particular regions of the tissue 17.
Experience shows that structures such as are portrayed here are well suited to stimulation or sensing of regions of tissue that are millimeters in size. For some applications such as cardiac pacing in human subjects, the millimeter-scale regions are exactly what is desired.
But for some diagnostic and therapeutic applications, it is needed or even required that the region of tissue being stimulated or sensed be on the order of a few hundred microns. If only ways could be found to stimulate and sense such very small regions, it might be possible to sense phenomena on the cellular level, perhaps as specific as the firing of an individual neuron. It might be possible to stimulate similarly small regions. Electrical stimulation might permit treatment, for example, of movement disorders such as Parkinson's and dystonia.
It would be highly desirable, however, that insertion of a lead for the purposes discussed here be done once and not more than once. Each insertion can cause trauma to tissue. If a lead were inserted, and later needed to be removed so that a different lead could be inserted (for example with a goal of slightly different electrode positioning) this would cause otherwise unneeded trauma to the nearby tissue. If on the other hand, a lead could be provided that permits great flexibility of use later, this would reduce how often a lead removal and replacement would be called for.
It is also highly desirable if such a lead could be as thin as possible, since a thinner lead is easier to insert and will cause less trauma to nearby tissue.
It has not, heretofore, been possible to achieve fully the desirable aims just discussed, particularly when other goals such as biocompatibility and physical reliability are also imposed.